The objective is to determine the crystal structures of neurotoxins from the venon of the scorpion Centruroides sculpturatus Ewing. Scorpion toxins are small basic proteins that interact with the sodium channels of excitable membranes. The structure will be determined using the techniques of protein crystallography. These studies will include refinement of the variant-2 toxin. Efforts will be made to grow large crystals of other toxins, with particular emphasis on toxin III, IV and V. The results of these studies will be used to establish structure/function relationships for the scorpion neurotoxins.